Inefficiency of conversion of seed into market-ready mussels in New Zealand's Greenshell™ mussel (Perna canaliculus) industry

Abstract

The inefficient conversion of seed mussels, or ‘spat’ into market-ready mussels is a major problem for mussel aquaculture operations worldwide, where sustained crop losses throughout the production cycle severely disrupt production and ultimately constrain industry growth. However, despite the severity of the problem for individual mussel farm operators, few studies have sought to examine this inefficiency on an industry-wide scale to assess the broader extent of the biological and economic losses. The Greenshell™ mussel (Perna canaliculus) industry is New Zealand's largest and most valuable aquaculture industry, and yet despite its success, the industry remains extremely inefficient at converting spat into market-ready adult mussels. Consequently, this study compiled and compared historical industry-wide data on the harvesting of spat with national statistics on the production of adult mussels by the aquaculture industry. The results of the analyses show that despite substantial increases in the harvesting of wild spat over the last 10 years, the production of market-ready mussels from the industry has not increased concordantly, remaining largely static at around 90,000 t, amounting to around 1.78 billion adults a year during this period. From 2015 to 2020 on average, 344 billion spat were harvested from the wild each year, yet <1% of these were retained on Greenshell™ farms from seeding out through to final harvest. Careful evaluation of historical data reveals the efficiency of converting seeded Greenshell™ spat to harvested market-ready mussels has halved over the last 30 years, with the cause of this marked decline uncertain. These results highlight the inefficient nature of the Greenshell™ industry and show that improving production efficiency by even a small margin would result in substantial production gains for the industry.